Given enough chances, every hiring manager will eventually hire someone incompetent – it’s as inevitable as death and taxes. And just as fun.

Some managers notch their first bad hire quickly, while others might go years before their first major hiring mistake. But if you hire enough people, eventually you'll pick someone who doesn't work out.

To boost the chances of preventing that hiring misstep, there's one easy tactic everyone should take in an interview: Stop asking candidates to evaluate their own abilities.

Here’s why. Underskilled candidates consistently overrate their abilities, and more skilled candidates consistently underrate their abilities. There’s even a name for this: the Dunning-Kruger effect, a psychological research finding that the poorest performers are the least aware of their own incompetence.

Here's an example: Let’s say you have two candidates applying for an open position. You ask both job applicants during the interview, ”On a scale from one to 10, how proficient are you with Excel?”

The highly skilled person will typically rate themselves lower on the scale than the less-skilled person. It may sound bizarre, but once you look for it, you’ll see it everywhere.

Setting standards

Top performers set higher standards for their own performance, so they judge themselves more harshly than low performers. The more candidates know about Excel, the more they realize how much they do not know about Excel. Consequently, the better people will typically underrate their expertise on self-evaluations.

Bob Corlett writes about innovation, staffing, leadership and performance management for The Business Journals. He is a founding member of the Editorial Advisory Board for The HR Examiner and the founder and president of Staffing Advisors, an executive search firm located near Washington DC.